Hamish A. McGowan

Modeling the impact of historical land cover change on Australia's regional climate

The Australian landscape has been transformed extensively since European settlement. However, the potential impact of historical land cover change (LCC) on regional climate has been a secondary consideration in the climate change projections. In this study, we analyzed data from a pair of ensembles (10 members each) for the period 1951–2003 to quantify changes in regional climate by comparing results from pre-European and modern-day land cover characteristics. The results of the sensitivity simulations showed the following: a statistically significant warming of the surface temperature, especially for summer in eastern Australia (0.4–2°C) and southwest Western Australia (0.4–0.8°C); a statistically significant decrease in summer rainfall in southeast Australia; and increased surface temperature in eastern regions during the 2002/2003 El Nino drought event. The simulated magnitude and pattern of change indicates that LCC has potentially been an important contributing factor to the observed changes in regional climate of Australia.

Identifying regional dust transport pathways: ­application of kinematic trajectory modelling to a trans-Tasman case

PI kinematic trajectory model is used to investigate potential pathways of dust transport from Australia to New Zealand. Historically, these have been assumed to follow rather direct west-east trajectories spanning 2 to 3 days, often resulting in red snow events in the Southern Alps of New Zealand. However, results from the present study which examined the route taken by air parcels originating in southern Australia during dust storms on 24 and 25 May 1994, indicate that trans-Tasman dust transport trajectories are more diverse than previously thought, and display considerable variation during single events. These mon divergent pathways tie in more closely with aeolian dust sedimentation patterns identified by ocean coring in the Tasman Sea, and may account for the deposition of Australian dust on sub-Antarctic islands located well south of the Australian continent. Copyright 2000 John Wiley Sons, Ltd.

Atmospheric pollutants in alpine peat bogs record a detailed chronology of industrial and agricultural development on the Australian continent

Two peat bogs from remote alpine sites in Australia were found to contain detailed and coherent histories of atmospheric metal pollution for Pb, Zn, Cu, Mo, Ag, As, Cd, Sb, Zn, In, Cr, Ni, Tl and V. Dramatic increases in metal deposition in the post-1850 AD portion of the cores coincide with the onset of mining in Australia. Using both Pb isotopes and metals, pollutants were ascribed to the main atmospheric pollution emitting sources in Australia, namely mining and smelting, coal combustion and agriculture. Results imply mining and metal production are the major source of atmospheric metal pollution, although coal combustion may account for up to 30% of metal pollutants. A novel finding of this study is the increase in the otherwise near-constant Y/Ho ratio after 1900 AD. We link this change to widespread and increased application of marine phosphate fertiliser in Australias main agricultural area (the Murray Darling Basin).

Impact of historical land cover change on daily indices of climate extremes including droughts in eastern Australia

There is growing scientific evidence that anthropogenic land cover change (LCC) can produce a significant impact on regional climate. However, few studies have quantified this impact on climate extremes and droughts. In this study, we analysed daily data from a pair of ensemble simulations using the CSIRO AGCM for the period 1951–2003 to quantify the impact of LCC on selected daily indices of climate extremes in eastern Australia. The results showed: an increase in the number of dry and hot days, a decrease in daily rainfall intensity and wet day rainfall, and an increase in the decile‐based drought duration index for modified land cover conditions. These changes were statistically significant for all years, and especially pronounced during strong El Nino events. Therefore it appears that LCC has exacerbated climate extremes in eastern Australia, thus resulting in longer‐lasting and more severe droughts.

Reconstructing annual inflows to the headwater catchments of the Murray River, Australia, using the Pacific Decadal Oscillation

Full-text is free to read on publisher website. The Pacific Decadal Oscillation (PDO) is a major forcing of inter-decadal to quasi-centennial variability of the hydroclimatology of the Pacific Basin. Its effects are most pronounced in the extra-tropical regions, while it modulates the El NiA±o Southern Oscillation (ENSO), the largest forcing of global inter-annual climate variability. PalaeoPDO indices are now available for at least the past 500 years. Here we show that the >500 year PDO index of Shen et al. (2006) is highly correlated with inflows to the headwaters of Australias longest river system, the Murray-Darling. We then use the PDO to reconstruct annual inflows to the Murray River back to A.D. 1474. These show penta-decadal and quasi-centennial cycles of low inflows and a possible 500 year cycle of much greater inflow variability. Superimposed on this is the likely influence of recent anthropogenic global warming. We believe this may explain the exceptionally low inflows of the past decade, the lowest of the previous 529 years. Copyright 2009 by the American Geophysical Union.

Aeolian dust transport and deposition by foehn winds in an alpine environment, Lake Tekapo, New Zealand

Abstract Observations from an automatic weather station and anemograph network are used in conjunction with recorded dust deposition rates to identify principle sources of wind blown dust within an alpine lake basin. Meteorological observations made throughout the study indicate that foehn windstorms provide ideal conditions for the initiation of aeolian processes, including dust storm genesis. A mean wind speed during foehn windstorms of 7.5 m s −1 at 2.65 m above the surface was observed to initiate entrainment of dust particles from geomorphically active areas within the lake basin, particularly from the dry braid channels of glacier fed rivers, exposed lacustrine deltas and degraded tussock grasslands. This threshold entrainment velocity is similar to others presented within the international literature for such surface types. A diurnal modulation of meteorological parameters monitored during foehn wind events suggests that aeolian processes, such as dust entrainment, are most likely to occur from late morning to early evening. However, where topography enhances wind speeds, for example by channelling airflow down river valleys, favourable conditions for dust entrainment may prevail throughout the night in the absence of precipitation. Potential dust roses were determined for two sites within the lake basin. The dust roses supported anecdotal and observational evidence of principle dust sources within the study area, and appear to be an effective tool for identifying the potential hazard to a particular location from blowing dust, once the physical trigger conditions for dust entrainment are known. This requires detailed and concurrent monitoring of meterological variables in association with dust transportation and deposition rates, especially in complex terrain where many micro-climates often exist.

Foehn Winds in the McMurdo Dry Valleys, Antarctica: The Origin of Extreme Warming Events

Foehn winds are warm, dry and gusty downslope winds resulting from the topographic modification of the airstream in the lee of mountain barriers. They are a climatological feature common to many of the world’s mountainous regions, however, detailed investigations into foehn winds in polar regions and their effects on environmental processes are rare. In the McMurdo Dry Valleys (MDVs) of Antarctica, frequent episodes of strong foehn winds are experienced. Here they cause dramatic warming at onset and are suspected to significantly affect landscape forming processes, however, no detailed scientific investigation of foehn in the MDVs has been conducted. As a result, they are often misinterpreted as adiabatically warmed katabatic winds draining from the Polar Plateau. This thesis integrates observations from surface weather stations, numerical model output from the Antarctic Mesoscale Prediction System (AMPS), hydrological data and remote sensing techniques to understand the dynamics and influences of foehn wind events in the MDVs. Results show that foehn winds in the MDVs are caused by topographic modification of south-southwesterly airflow which is channelled into the valleys from higher levels. Modelling of a winter foehn event identifies mountain wave activity similar to that associated with mid-latitude foehn winds. These events are found to be caused by strong pressure gradients over the mountain ranges of the MDVs related to synoptic-scale cyclones positioned in the Amundsen/Ross Sea region. Importantly, these results clarify that a foehn mechanism is responsible for the strong warm wind events in the MDVs and that the influence of katabatic surges from the Polar Plateau as an origin or triggering mechanism of events is minimal. A 20-year climatology of foehn winds is presented from observational records in the MDVs. The intra- and inter-annual frequency and intensity of foehn events varies in response to the position and frequency of cyclones in this region. These cyclones are well known to be influenced by the El Nino Southern Oscillation (ENSO) and the Southern Annular Mode (SAM). Statistically significant relationships are found between the SAM and foehn wind frequency during the Antarctic summer and autumn months whereas ENSO only holds significant correlations with winter air temperatures in the MDVs. Foehn winds are a major climatological feature of the MDVs with their frequency and duration affecting the region’s temperature records and their trends. Accordingly, analysis of the region’s weather and climate records and predictions of future impacts of climate change on the MDVs is incomplete without consideration of foehn winds and their influence. In the past, the influence of foehn wind events on landscape processes of this polar desert has not been well understood. Hydrological data and remote sensing techniques are used to quantify the influence of foehn winds on environmental processes in the MDVs. Foehn winds frequently cause summer temperatures to rise above 0°C leading to extensive melt and thaw in the MDVs. Sublimation, stream discharge and snow persistence are shown to be significantly influenced by foehn winds and the effects of foehn are demonstrated to outlive the duration of the event. It is concluded that foehn winds in the MDVs are the major cause of contemporary landscape change. Future changes in the MDVs landscape may be linked to variability in teleconnections (e.g., SAM and ENSO) and their influence on synoptic circulation patterns that drive cyclone activity in the Ross Sea region and the foehn wind regime.

Evidence of ENSO mega-drought triggered collapse of prehistory Aboriginal society in northwest Australia

The Kimberley region of northwest Australia contains one of the Worlds largest collections of rock art characterised by two distinct art forms; the fine featured anthropomorphic figures of the Gwion Gwion or Bradshaw paintings, and broad stroke Wandjina figures. Luminescence dating of mud wasp nests overlying Gwion Gwion paintings has confirmed an age of at least 17,000 yrs B.P. with the most recent dates for these paintings from around the mid-Holocene (5000 to 7000 yrs B.P.). Radiocarbon dating indicates that the Wandjina rock art then emerged around 3800 to 4000 yrs B.P. following a hiatus of at least 1200 yrs. Here we show that a mid-Holocene ENSO forced collapse of the Australian summer monsoon and ensuing mega-drought spanning approximately 1500 yrs was the likely catalyst of this change in rock art. The severity of the drought we believe was enhanced through positive feedbacks triggered by change in land surface condition and increased aerosol loading of the atmosphere leading to a weakening or failure of monsoon rains. This confirms that pre-historic aboriginal cultures experienced catastrophic upheaval due to rapid natural climate variability and that current abundant seasonal water supplies may fail again if significant change in ENSO occurs.

Niveo-eolian Sediment Deposits in Coastal South Victoria Land, Antarctica: Indicators of Regional Variability in Weather and Climate

Abstract A 35 year chronology from 1965 to 2000 of the deposition of wind-blown sediment is constructed from snowpits for coastal southern Victoria Land, Antarctica. Analysis of local meteorology, contemporary eolian sedimentation, and mineralogy confirm a Victoria Valley provenance, while the presence of volcanic tephra is ascribed to an Erebus volcanic province source. Winter foehn winds associated with anticyclonic circulation are considered responsible for transporting fine-grained sediment from the snow- and ice-free Victoria Valley east toward the coast, while cyclonic storms transport tephra north along the Scott Coast. No trend could be identified in the occurrence of either tephra or wind-blown sediments sourced from the Victoria Valley and retrieved from the snowpits excavated on the Victoria Lower and Wilson Piedmont Glaciers. We infer this to indicate that the region has not undergone a significant change in weather patterns for at least the last 35 years. Our results also confirm the McMurdo Dry Valleys as a regionally significant source of wind-blown sediment.

Approaches to modelling land erodibility by wind

Land susceptibility to wind erosion is governed by complex multiscale interactions between soil erodibility and non-erodible roughness elements populating the land surface. Numerous wind erosion modelling systems have been developed to quantify soil loss and dust emissions at the field, regional and global scales. All of these models require some component that defines the susceptibility of the land surface to erosion, ie, land erodibility. The approaches taken to characterizing land erodibility have advanced through time, following developments in empirical and process-based research into erosion mechanics, and the growing availability of moderate to high-resolution spatial data that can be used as model inputs. Most importantly, the performance of individual models is highly dependent on the means by which soil erodibility and surface roughness effects are represented in their land erodibility characterizations. This paper presents a systematic review of a selection of wind erosion models developed over the last 50 years. The review evaluates how land erodibility has been modelled at different spatial and temporal scales, and in doing this the paper identifies concepts behind parameterizations of land erodibility, trends in model development, and recent progress in the representation of soil, vegetation and land management effects on the susceptibility of landscapes to wind erosion. The paper provides a synthesis of the capabilities of the models in assessing dynamic patterns of land erodibility change, and concludes by identifying key areas that require research attention to enhance our capacity to achieve this task.